The present invention relates to a manually operated lever drive system for wheelchairs that attaches as an after-market application to the primary drive wheels. Manually powered wheelchairs are often used by people who have physical impairments that diminish the strength available for propelling the wheelchair. The fundamental physical requirements of an individual utilizing a manual wheelchair are inherently contrary to abilities and limitations of the impaired because in general, and by design, manually powered wheelchairs require the user to grasp a circular hand-ring that is attached to the wheelchair drive wheel. To move the chair, the user is required to grip this ring and apply manual pressure to rotate the hand-ring and corresponding wheel in the desired direction of travel. Since the grip is concentric with the wheel, and rotates as the wheel rotates, the user can apply maximum force to the rotating grip for only a portion of the rotation of the wheel. The ring then rotates out of the reach of the user, and the user needs to release the circular ring and grab it again at another point on the circumference of the ring, and reapply muscular pressure to keep moving. In addition to the circular hand-ring, there are a number of existing variations of the circular hand-ring, i.e., a hand-ring with protruding knobs located along the circumference of the hand-ring for those individuals not possessing an ability to grip a standard hand-ring.
There are many systems for driving wheelchairs, which include various mechanisms with gears and sprockets, a plurality of wheels, drive linkages and cables, motors, and other methods. In U.S. Pat. No. 4,523,769, Glaser uses a lever/ratchet mechanism to drive gears for propulsion. Taylor (U.S. Pat. No. 6,234,504) uses levers to drive sprockets, connected to the drive wheel via chains, similar to Banzi (U.S. Pat. No. 6,325,398). In U.S. Pat. No. 6,634,663, Mitchell uses a lever to operate a crank handle that presses on circular handrails when pressure is applied. In U.S. Pat. No. 6,325,398, Banzi discloses a chain transmission. Drake (U.S. Pat. No. 5,941,547) uses one-way bearing clutches, but attaches the bearings and drive levers to a pivot point on the wheelchair frame, moving the lever attachment point away from the center of gravity of the chair, requiring a drive cable to convert lever motion to rotational motion. Sheaffer, in U.S. Pat. No. 3,994,509, cites the use of overrunning clutches, but connects them to a chain to drive the wheel(s).
Oxford (U.S. Pat. No. 5,303,945) discloses a ratchet wrench to apply motive power. Oxford's use of a ratchet wrench allows the user to maintain a grip on the drive handle. However, it requires the user to release the drive handle to operate a lever to control a shifting mechanism. Since the shifting lever rotates with the wrench, it changes rotational location with every stroke. Thus, the user has no knowledge of the rotational position of said shifting lever at any given moment, and will need to either look at the wheel or search manually to locate said shift lever. Additionally, a ratchet wrench comprises a plurality of gear teeth which click past a spring-loaded pawl when the handle is returned to the starting position to reapply motive power, such that the user is accompanied by a clicking noise during each rewinding stroke, or while in neutral and the chair is in motion, such as while coasting or rolling downhill. The prior art lacks the ability to provide a silent means of propulsion, so the user of a lever-driven wheelchair is not accompanied by noise whenever the user moves the chair.
Furthermore, when a ratchet wrench is used, there is some distance of travel through which the mechanism must be moved before the ratchet engages and forward travel is again possible after the rewind stroke. This distance, sometimes characterized as “play”, is due to the inherent design of a ratchet wrench. Therefore, traveling short distances require the handle to travel distances out of proportion to the desired distance of travel, making small position adjustments difficult when using a drive system comprising a ratchet wrench. There is a need to provide a lever driven mechanism with no play, so precise chair positioning is easy.
Another problem with Oxford's approach is the difficulty in using the levers on either side of the chair independently. If the mechanism remains “tight”, the various elements comprising the “inverted U-shaped member” will not easily slide relative to each other, which is required for operation. If they are loose enough so they can easily slide past each other and allow independent use of the levers, there will be more play in the mechanism, which will make the chair noisy, and less efficient to operate. There is no provision to flex individual, dedicated handles towards the user, against the surface of the wheel hand-ring, for frictional braking and/or steering. Another, more glaring problem with Oxford's approach is that the U-shaped member has to be removed each time a user needs to enter or exit the chair, then re-assembled when the user needs to re-enter the chair. The prior art fails to provide a system that is easy to use and easy to access, so a user can sit down in the chair and immediately start moving the chair by pressing on the lever handles, with no adjustments required, no mechanisms to move out of the way, no switches to locate to place the drive system in neutral, and no gears, cables, sprockets, or any other exposed hardware to present a physical hazard to the impaired.